Scrollview not displaying all elements of a Relative Layout

Hi guys I'm very new to the android world and I've been having a problem with a ScrollView in my android application. The problem occurs when I change the orientation of the screen from portrait to landscape and the Sign in button is not displayed. It could be the due to the sign up button being displayed at the end of the layout. Any help would be appreciated.

The login_layout.xml is as follows:

<?xml version="1.0" encoding="utf-8"?>
<ScrollView xmlns:android="http://ift.tt/nIICcg"
android:scrollbars="vertical"
android:layout_width="fill_parent"
android:layout_height="fill_parent"
android:fillViewport="true"
android:layout_weight="1">

<RelativeLayout
    android:orientation="vertical" android:layout_width="fill_parent"
    android:layout_height="fill_parent" android:background="#ff2b8bff">

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Sign in"
        android:id="@+id/signInButton"
        android:background="#fffffbfd"
        android:onClick="signIn"
        android:layout_below="@+id/usersPassword"
        android:layout_centerHorizontal="true"
        android:layout_marginTop="52dp" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textEmailAddress"
        android:ems="10"
        android:id="@+id/usersEmail"
        android:layout_marginTop="31dp"
        android:layout_below="@+id/bourguestLogo"
        android:layout_centerHorizontal="true" />

    <EditText
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:inputType="textPassword"
        android:ems="10"
        android:id="@+id/usersPassword"
        android:layout_marginTop="35dp"
        android:layout_below="@+id/usersEmail"
        android:layout_alignStart="@+id/usersEmail" />

    <Button
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:text="Sign up"
        android:id="@+id/signUpButton"
        android:onClick="changeLayout"
        android:background="#ffff2f14"
        android:layout_alignParentBottom="true"
        android:layout_alignParentStart="true"
        android:layout_alignParentEnd="true" />

    <ImageView
        android:layout_width="wrap_content"
        android:layout_height="wrap_content"
        android:id="@+id/bourguestLogo"
        android:src="@drawable/waiter"
        android:layout_marginTop="88dp"
        android:layout_alignParentTop="true"
        android:layout_centerHorizontal="true" />

</RelativeLayout>
</ScrollView>